THIS invention relates to conveyor belt scrapers.
To avoid spillage, conveyor belts are not generally loaded to full capacity. Thus the material which is being conveyed on the belt is located on the central region of the upper run of the belt and very little, if any, material is in contact with the lateral extremities of the belt. On the return run of the belt, one or more scrapers are arranged to scrape any adhering material from the belt surface. For instance, a scraper may be positioned generally below the head or discharge roller where the belt is initially reversed on the return run.
Known belt scrapers either have a one-piece or segmented scraper blade, the latter being composed of a series of side-by-side blade segments, arranged to scrape the full width of the belt on the return run. Because little if any material was initially in contact with the lateral extremities of the belt on the upper run, the ends of the scraper blade are required to perform only a minimal scraping action. The central region of the scraper blade is required to perform the majority of the scraping action. The end result is that the ends of the blade are subjected to less abrasive wear than the central region of the blade, and hence wear down less rapidly.
In most known scraper systems the blade is initially urged upwardly against the belt with a predetermined force so that the desired scraping action can be achieved. The blade is usually mounted fast on a rigid cross-bar spanning between adjustable structures located to the sides of the belt. The adjustable structures can be adjusted to move the cross-bar, and hence the scraper blade, upwardly against the belt. However, the above-mentioned phenomenon of differential rates of wear between the central and end regions of the blade makes it impossible in conventional practice to adjust the crossbar in such a way that all regions of the worn blade are loaded equally against the belt. Since most of the scraping action takes place in the central region of the belt, it often happens that the ends of the blade are excessively loaded in order to obtain an acceptable upward load on the more worn central region of the blade or, in the case of a segmented blade, on the more worn, centrally located blade segments.
EP 0 486 112 A1 describes a conveyor belt scraping apparatus in which a series of scraper blade segments are carried by vertical shafts which are located slidably in tubular guides and which are biased upwardly against the belt by inflation of an elastic tube against which the lower ends of the shafts bear. A serious drawback of this arrangement is the fact that the shafts can easily jam in the guides, particularly if any dirt is allowed to enter the guides.
WO 93/04959 describes a somewhat similar arrangement in which individual blade segments are urged upwardly against the belt by individual gas springs, possible fouling of the individual mechanisms once again being a potential problem.
Another proposal, described in GB 2 165 200 A, is an arrangement in which a non-segmented blade is connected at each end to a pivoted linkage which is acted upon by a gas spring which operates the linkage, through a crank, in a manner to urge the blade against the belt. The problem here is that the blade is loaded only at its ends, resulting in non-uniform scraping of the belt and/or wear of the blade, as described above.